<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    /* 
    box-sizing用来设置盒子模型中宽高的行为
    
    content-box
    口padding、border都布置在width、height外边

    border-box
    口 padding、border都布置在width、height里边
    */
    .box1{
        box-sizing: content-box;
        width: 100px;
        height: 100px;
        background-color: #f00;
        padding: 30px;
        border: 10px solid orange;
    }
    .box2{
        width: 100px;
        height: 100px;
        background-color: rgb(208, 255, 0);
        padding: 30px;
        border: 10px solid orange;
        box-sizing: border-box;
    }
</style>
<body>
    <div class="box1"></div>
    <div class="box2"></div>
</body>
</html>